Repeater-circuits



L. ESPENSCHIED.

REPEATER cmcuns.

APPLICATION FILED DEC. 19, 1918 1,3?8, 1'70 D Patented May 17, 1921.

3 SHEETS-SHEET I.

. ATTORNEY L. ESPENSCHIED.

BEPEATER CIRCUITS.

APPLICATION FILED DEC. 19. 1918.

Patented May 17 1921.

3 SHEETS-SHEET plllll mm l mum WWW? ZloyeZ A TTORNEY L. ESPENSCHIED.

REPEATER CIRCUITS.

APPLICATION FILED DEC. 19. 1918.

1,378,170. Patented May 17,1921

3 SHEETS-SHEET 3.

INVENTOR.

Zlaydils enscfizd i BY 0 A TTORNEY v UNITED STATES PATENT OFFICE.

moynnsrnnscnrnn, or HOLLIS, NEW YORK, Assmnon r0 AiirEnI'cAN TELEPHONE AND rnnnennrn COMPANY, A conronarron or nnw' onx;

) REPEATERr-CIRCUITS.

To all whom it may concern: 7

Be it knownfthat I LLOYD Esrnusonmn, residing. at Hollis, liiong Island, in the county of Queens and State of New York, have invented certain Improvements in Repeater-Circ 'ts,"of which the following is a specification. This invention relates to composite or other signaling systems carrying two or a more signal currents-of different character or frequency, and more especially to the amplification of signal currents in such systerns. In signaling circuits carrying, for instance, both telephone and telegraph cur: rents, the amplification of the telegraph signals has l eretofore been accomplished by mechani hamplifiers in a portion of the circuit not "carrying telephone currents. The desirabilityof amplifying both sets of signals in sucha system by a' single instrument is obvious, and it is especially advantageous'where both use the-same metallic circuit in both directions and where the different sets of signal impulses are reduced to the same order of magnitude but so far as I am aware no such anarrangement has ever been used. In the employment of the thermionic amplifiers, which are by far the most eflicient for telephone amplification, it is highly desirable, if not necessary, to interpose a transformer between the amplifier and the line on either side,

from the lower impedance of the been used for this purpose do not however transmit current of the kind used in telegraphy and other signaling systems. I

The tendency toward the use of m cal repeaters in separate circuits metallically connected with the line, for amplifying telegraphic currents, is a natural result of the common habit of looking upon the telegraph current as a direct current. It may however properly be regarded as a wave composed of a number of sinusoidal currents of different frequencies. In this sense the action of the mechanical repeater is one of reforming the telegraph wave. The input side receives an atte uated current building up relatively slowly, while the output side transmits a new wave of greater quencies by to separate the ,high impedance circuits of the amplifier lines and to isolate from theline the'batteries asso-* ciated with the amplifier. j-The transformers which have telegraph Specification of Letters Iatent. Patented May 1'7, 1921, Application med December 19, 1918. Serial 1%. 267,527.

naling waves as encompassing a band of frequencies in the same way that we speak of telephone currents occupying a band of frequencies. The steepness of the telegraph wave is then an indication of the width of the frequency band comprised. V

The action of the mechanical amplifier of telegraph currents -may be considered as one of receiving currents representing a band of frequencies of which the higher have suffered a disproportionate attentuation by transmission over the line, and of retransmitting a corresponding band of frequencies in which the higher frequencies are supplied in greater proportion than in the received current and .in proper phase relations, so that the Wave is reformed. The repeating action may be regarded as one of equalizing the current amplitudes by amplifying relatively more the higher frequency components and of readjusting the'phase relations. The mechanical relay, however, in its output side generates a square wave which includes currents of frequencies within the telephone range and higher than is essential for good speeds in telegraph signaling; These interfere with the telephone transmission and it is, therefore, necessary in superimposing the relay output upon a telephone circuit to suppress the higher frewell known composite set. Thus the mechanical'relay actually equalizes too much, or over equalizes, for use on composited circuits. Considering the mechanical repeater broadly, there may be said to be two steps, one of energy reimbursement, entailing overequalization, and the. other one of compensation for the over-equalization, effected by y y the composite set.

chani- It'is one of the main objects of the present invention to overcome these difficulties and defects in theamplification on -com-' lposite' lines and to avoid the inherent limitations of mechanical amplification by sinplo'ying the thermionic amplifier used for the telephone currents to amplify also the or other. currents in the circuit,

means of selective circuits-the combining therewith a composite transformer and attentuation equalizing elements suitable for dealing with all the signal currents. Provision is also made, where necessary, for carrying the D. C. component of the telegraph current around the amplifier.

In the form of the invention described below, two transformers are provided functioning over different frequency ranges, one transformer taking up the action at or near the pointwhere the other transformer leaves off. The invention contemplates, however,

, the use of a greater or less number of trans.

formers where desirable. A single transformer to cover the entire range of frequencies may be used where circumstances make it possible to secure .the desired efficiency for all signal currents in this way.

A further feature of' the invention resides in controllin the relative efficiency with which the di erent frequencies comprising the telephone and telegraph or other transmission ranges are transmitted through they repeatengwith the object of compensating for the unequal transmission of these fre quencies over the transmission line itself,

The equalizing actlon can be introduced by equalizers individual t6 each ofthe super- I imposed channels or by an equalizer common to all channels and capable of equalizing throughout the entire frequency range involved. Equalizing the channels individually requires that additional frequency discriminating circuits be associated with the equalizers in order that they be confined to theparticular range of frequencies for which each is intended, just .as in the case of input' and output transformers operating to transform only in a prescribed range of frequencies. The means for doing this are shown subsequently in connection with the accompanying figuresa It should here be noted that division of the frequency range between equalizers need'not necessarily be coincident with the division 1 of the frequency range between the communication channels. In fact, where-discreet. equalizers are'employed for individual= channels, their effects may overlap to form substantially continuous equalization throughout the entire frequency range. This is desirable because it enables the range of frequencies between the tele raph and telephone channels to be use ully employed either by operating the telegraph as a higher speed channel andthereby using a broader frequency band, or by superimposing one or more other signaling channels in the rangeof frequencies between the telegraph and j telephone channels. Such an alternating current channel may be employed either for telegraph signaling or for telephone signaling. In fact it is common in the operation of composited telephone and telegraph circuits -to employ for telephone signaling a channel of 133 cycles which is in the range referred to. It is desirable to repeat this channel likewise in the common amplifier and to adjust the transmission of it over the 'en'tire system in va manner similar to the transnfission adjustment of the other. chan-- nels, z. e., by suitable equalization.

two methods of equalization.

the, equalization.

The invention will be more fully understood by reference to the accompanyingdrawings,in which-Figure 1 ically one embodiment thereofapplied to a one-way repeater, Fig. 2 shows an arrangement for a two-way repeater embodying the invention, Fig. 3 shows a modification and shows diagrammat- Figs. 4 and 5 show curves illustrating the f In Fig. 1 the incoming circuit is indicated at 11 and the outgoing circuit at 22. The circuit 1 is connected with the primary windings of the transformers 3 and 4, which may be regarded. as together constituting a composite input transformer. The windings at 3 and at 4 are on separate core as indicatedvby the dotted lines and are'designed,'

respectively, for the frequencies represented in the telephone and telegraph currents. The windings of theseparate transformers may be either. in series or parallel. Where they are in series asshown on the drawing it is preferable, in order to avoid any unbalance in the'telephone circuit, to divide the windings of onejof them (here shown as the transformer 3) into'two equal sections (5 and 6) between which the windings of the other transformer are connected. The attenuation equalizers 7 and 8 for the telephone currents and telegraph currents re spectively, are alsopreferably connected between the halves of the primary windings of their respective transformers for avoidillgunbalance in the system. The equalizer for the telephone currents may however, if arallel with its desired be connected in I transformer, and no unba ance 1s produced .by this arrangement. These equalizers may assume a variety of forms depending upon circuit conditions and the character of the. 106

currents, that shown for the telephomreufi rents .consisting .of resistance 9a part, 9' of which is shunted by an inductance '10 and capacity 11. The equalizenshown for the telegraph currents comprises merely a capaclty 12 and a resistance13 in parallel. The transformer itself, especially with the lower frequencies such as the telegraph, may

by proper design, be made to cooperate 1n these devices depends upon the values given their various elements and, as is well understood, their effect in general is to'increase the attenuation of the lower frequencies to compensate for the greater attenuation of transmitting circuit proper. It may be noted here in passing that the use of such an equalizer is impractleal with-mechanical repeaters because it weakens the already weak current to a point where it is insufficient 'to satisfactorily operate a repeater of that type.

The selective efi'ect of A condenser 14-:is placed in series with the attenuation equalizer 7 for preventing the telegraph currents from passing through it 130.

through the telephone equalizer into the teletransformer .ing all frequencies above a very low quency,

graph transformer by the leakage inductance of said transformer. This inductance will be sufliciently. large in ordinary cases. If, however, it is not, or if the internal capacities between windings are such as ,toof telephone currents,

permit the passage additional inductances sufficiently large to exclude the telephone currents will be added in series with the transformer windings.

The secondary windings of the transformers 3 and 4 are connected in the same relation, here shown as series, as their primaries. When connected in series as shown a condenser 15 is connected in shunt to the secondary winding of transformer 4 for affordinor the high, frequency telephone cur-- rents a path around the high inductance of that winding.

The input side of the thermionic amplifier 16 is connected to the output side of the composite transformer 3-4 and the output side of the amplifier is connected to the primary windings of a second compositetransformer 17-18,, which is ingeneral similar to the transformer in the input circuit, the transformer'17 being designed for transmitting the telephone-currents and the transformer 18 the telegraph currents. With the series arrangement of these transformers, here shown, balance is maintained as in the case of the input transformer by dividing the windings of one of the transformers in the middle and connecting the windings of the other between the halves. The attenuation equalizers are omitted in the output circuit but a condenser corresponding to condenser 15 in the input circuit is connected in parallel with each. of the windings of the the free passage of telephone currents.

By this arrangement, the telephone impulses will be transmitted and amplified as usual, the various frequencies comprised within the telephone range being equalized in the circuit 7, and the alternating current component of the telegraph current, inclpdsay two cycles, will be transmitted through the transformer 4, amplified at 16 and re-introduced into the transmission line by the transformer 18; the attenuation of the various frequencies comprised within the telegraph range being equalized in the circuit 8 as in the case of the telephone currents. If it is desired to preserve the direct current component of the telegraph waves, this may be done by connecting high inductance shunts 21 around the transformer and amplifier as indicated on the drawing. When these are used large capacities 22 should be connected into the conductors ondary windings 32, 33',

18 as at 19 and 2.0, to permit 1-1, 2-2 between applied to a two-way two repeater circuit which are now the general characteristics of too well-known to require. detailed explanation. The amplifiers 23 and 24 transmit energy in opposite directions lines 24 and 25. The input circuit of each repeater is connected to through a composite'transformer, 26 and the connection of the high inductance shunts 21 and the transbetween the one of the lines I 27 respectively, provided 'with attenuation equalizers for the telephone and telegraph currents and corresponding with the apparatus shown in Fig. 1 between the line 1- -1 andth'eamplifier 16. v The output circuit of each repeater is connected to the other line through a special transformer hichcombines the functions of the output transformer of 1 and'those of the three winding transformer'commonly employed in repeater circuits. of this type. The primary windings of this transformer are indicated at 28, 29, 30 and 31 of which 28 and-29 together constitute the telephone winding and 30 and 31 the telegraph winding. Thesec- 34 and 35 are located in the opposite :sid'esof the line as usual, the windlngs 32 and 33 together constituting the telephone windin s and the windings 34 and 35 the telegrap side of the amplifiers are taken off at the center of the composite windings, i. e. the point where the halves of the telegraph transformer 30 and 31 join.

As in Fig. 1, the windings of the telegraph transformer are shunted by condensers 36 and 37 for permitting he free passage of the telephone currents." Theextremities of the two transformer windin 29 are con nected, to the artificial line as usual in this type of repeater. If the inductive shunts 21, are used around the amplifiers for carrying the direct currentcomponent of the telegraph wave, they will be connected directly to the respective circuits 24 and 25 in-the drawing, and theconand the transformer both telephone and teleefl'ectedf in one circuit 38,

"which is here shown as comprising elements to the separate one and telegraph 1. Here also, the

corresponding generall equalizers for the telep currents shown in Fig.

telephone transformer 39- 40 is interposedin all respects will intervene between these ifica-tion shown in Fig. 3' the windings. The taps for the circuit leading to the input telegraph currents, or the larger part t between the halves of the telegraph transformer 41-42. In general where a series arrangement is desired it is immaterial whether the telephone or the telegraph transformer be connected in the center.

If the telephone and telegraph channels are provided with separate attenuation equalizers, as in Figs. 1 and 2, there may be a band of frequencies between the telegraph and telephone frequencies which is unequalized as indicated in Fig 4 where frequency is plotted against attelfuation. The attenuation of an ordinary loaded line is as indicated by the curve a. The attenuation equalizer for the telephone currents will increase the attenuation of the. lower frequencies, down say to 300, as indicated by the dotted line b. For lower frequencies the attenuation may if desired drop ofl as indicated at 0 and the telegraph frequencies, say below 100, may then be equalized as indicated at d. This, of course, permits the telegraph frequencles to be equalized at an attenuation less than-that of the telephone frequencies. Where the two are equalized together, as in Fig. 3, or if separate equalizers are so designed, theattenuation for all frequencies will be the same as indicated by the dotted line e in Fig. 5.

It will be apparent that the arrangements above described permit of alnplifylngl the ere- '-of, without re-introducing, the high frequencies which in present practice must be again removed by composite sets. Moreover,

much greater amplification maybe secured by the use of the thermionic amplifier and the arrangement permits of amplifying both telephone and telegraph currents by a single device. w

The use of the telephone and telegraph frequencies for illustrating the nature of the present invention is not to be taken as limiting its scope to such frequencies although it is of peculiar value in connection with" telegraph. currents for reasons above indicated, and it will be understood that the invention islnot limited to the details of circuit arrangement herein disclosed as it will be obvious that various changes may be made without departing from the spirit of the invention.

of a main -line for simultaneously transmitting telephone and telegraph currents, an amplifier adapted to simultaneously amplify the line and the input and output circuits.

of the amplifier, and means for equalizing the attenuation of the frequencies within the telephone range and of the frequencies within thetelegraph range.

3. In a signaling-system, a combination of a main line for simultaneously transmitting telephone and telegraph currents, an amplifier adapted to simultaneously amplify both currents, a composite transformer connecting the amplifier with the line on either side, and provided with separate windings for transmitting telephone and telegraph frequencies respectively, and attenuation equal izers for the telephone and telegraph frequencies connected respectively between the halves of the telephone and telegraph transv former windings.

4. A composite transformer for use on composite. telephone and telegraph lines comprising separate windings for the telephone and telegraph frequencies respectively, the windings for one set of frequencies being connected between the halves of the windings forthe other set of frequencies, means for by-passing the telephone frequencies around the windings designed for the telegraph frequencies, and attenuation equalizers for the telephone and telegraph frequencies respectively, connected between the halves of the transformer windings designed for the corresponding fre quencies.

5. In a signaling system, the combination of a main line for simultaneously transmitting telephone and telegraph currents, a two-way repeater in said main line comprising a separate amplifier for transmitting current in each direction, three-winding transformers connecting the output circuits of the amplifiers with the lineeonductors leading in opposite direction, the secondaries of said transformers including like windings in the opposite sides of the line, conductors leading from the central points of said secondary windings and a composite transformer connecting said conductors with the input circuits of said amplifiers, and having separate windings adapted to transmit the telephone andtelegraph fre-' quencies respectively.

' 6. In a signaling system, the combination of a main line for simultaneously transmitting telephone and telegraph currents, a twoway repeater in said mam line comprising a separate amplifier for transmitting current in each direction, three-winding trans formers connecting the output circuits of the amplifiers with the line conductors leading in opposite directions, the secondaries of said transformers including like windings in the opposite sides of the lines,.conductors leading from the central points of said secondary windings, a composite trans.-

former connecting said conductors with the 7 input circuits of said amplifiers, and having separate windings adapted to transmit the telephone and telegraph frequencies respectively, the three-wmding transformers comprising separate windings for transmitting the telephone and telegraph frequencies respectively.

7. In a signaling system, the combination of a main line for simultaneously transmitting telephone and telegraph currents, an amplifier adapted for simultaneously amplifying both currents, inductive connections between the line and the input and output circuits of the amplifier comprising sections 'for transmitting the telephone and telegraph currents respectlvely, and means for by-passing the direct current component of the telegraph-current around the amplifier and its inductive connections.

of a main lme for simultaneously transmitting telephone and telegraph currents, an amplifier adapted to simultaneously amplify both currents, inductive connections between the line and the input and output circuits of the amplifier, comprisin sections for transmitting the telephone an telegraph frequencies respectively, high inductance shunts directly connecting the sections of the main line on opposite sides of the amplifier and it's inductive connections,

and condensers located in the main line 0011- ductors between their connection with the high inductive shunts and said inductive connections.

In testimony whereof, I have signed my name to this specification this seventeenth day of December, 1918.

' LLOYD ESPENSCHIED, 

